[PATCH] D158601: [Clang] Always constant-evaluate operands of comparisons to nullptr

[Corentin Jabot via Phabricator via cfe-commits]

cor3ntin created this revision.
Herald added a project: All.
cor3ntin requested review of this revision.
Herald added subscribers: cfe-commits, wangpc.
Herald added a project: clang.

even if we know what the result is going to be.
There may be side effects we ought not to ignore,

Fixes #64923


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D158601

Files:
  clang/docs/ReleaseNotes.rst
  clang/lib/AST/ExprConstant.cpp
  clang/test/SemaCXX/compare-cxx2a.cpp


Index: clang/test/SemaCXX/compare-cxx2a.cpp
===================================================================
--- clang/test/SemaCXX/compare-cxx2a.cpp
+++ clang/test/SemaCXX/compare-cxx2a.cpp
@@ -461,3 +461,21 @@
   template<typename T> bool f6() { return 0 < y6; } // expected-note {{instantiation of}}
   void g6() { f6<int>(); } // expected-note {{instantiation of}}
 }
+
+
+namespace GH64923 {
+using nullptr_t = decltype(nullptr);
+struct MyTask{};
+constexpr MyTask DoAnotherThing() {
+    return {};
+}
+
+constexpr nullptr_t operator++(MyTask &&T); // expected-note 2{{declared here}}
+void DoSomething() {
+  if constexpr (++DoAnotherThing() != nullptr) {} // expected-error {{constexpr if condition is not a constant expression}} \
+                                                  // expected-note  {{undefined function 'operator++' cannot be used in a constant expression}}
+
+  if constexpr (nullptr == ++DoAnotherThing()) {} // expected-error {{constexpr if condition is not a constant expression}} \
+                                                  // expected-note  {{undefined function 'operator++' cannot be used in a constant expression}}
+}
+}
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -13306,6 +13306,10 @@
     // C++11 [expr.rel]p4, [expr.eq]p3: If two operands of type std::nullptr_t
     // are compared, the result is true of the operator is <=, >= or ==, and
     // false otherwise.
+    LValue Res;
+    if (!EvaluatePointer(E->getLHS(), Res, Info) ||
+        !EvaluatePointer(E->getRHS(), Res, Info))
+      return false;
     return Success(CmpResult::Equal, E);
   }
 
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -170,6 +170,11 @@
   requires-expression. This fixes:
   (`#64138 <https://github.com/llvm/llvm-project/issues/64138>_`).
 
+- Expressions producing ``nullptr`` are correctly evaluated
+  by the constant interpreter when appearing as the operand
+  of a binary comparision.
+  (`#64923 <https://github.com/llvm/llvm-project/issues/64923>_``)
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D158601.552673.patch
Type: text/x-patch
Size: 2375 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20230823/f865a61c/attachment.bin>